Successful operation of communications and navigation equipments aboard an aircraft usually requires that they are capable of functioning satisfactorily in the ambient electronic noise that is usually found aboard an operational aircraft. A bothersome source of electronic interference that frequently must be tolerated is attributed to the numerous motor-generator combinations running at 400 hertz. Although these combinations are intended to operate precisely at 400 hertz, they all seem to vary their speed slightly so that the electonic interference created by them fluctuates about 400 hertz.
To date one technique uses three precise frequency synthesizers set at slightly different frequencies and the outputs are mixed together. The disadvantages of this approach are that, in addition to tying up three general purpose generators, the frequencies generated did not have the ability to slightly vary to represent the slight variation in the motor-generator speeds associated with these units on the aircraft. As a consequence, a realistic test and evaluation of the equipments could not be made in a more accurate portrayal of the electronic noise environment aboard an operational aircraft.
Thus, a continuing need exists in the state-of-the-art for a frequency generator for the designers of and maintenance crews for aircraft communications and navigation equipments that is capable of simulating the fluctuating electronic interference attributed to motor-generator noise sources aboard an aircraft.